Dosing pump with an electric motor

ABSTRACT

The metering pump comprises a synchronous motor which is stepped down via a mechanical gear and the rotation movement of the motor is converted into a stroke movement which drives the membrane pump. To the motor there is allocated an electronic control which may be activated by external impulses with regard to the delivery quantity. At the same time the control operates such that one always passes through a complete operating cycle of the pump if the nominal delivery quantity resulting on account of the received impulses is as large or larger than the quantity which the pump delivers in an operating cycle.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a metering pump according to the features specified in the introductory part of claim 1.

[0002] With metering pumps one differentiates essentially between two types of construction, the electromagnetically and the electromotorically driven ones. With the first construction type the control of the delivery quantity is effected via the frequency at which the stroke magnet is driven, wherein additionally the stroke volume as a rule may be changed by way of a mechanical setting screw, i.e. the delivery quantity per operating cycle. In contrast, with the electromotorically driven metering pumps of the type according the introductory part of claim 1 such a mechanical stroke adjustment is not regularly provided, it would indeed be technically comparatively complicated. With these pumps the oscillating movement of the pump is produced by a gear in the manner of a crank mechanism or a suitable block guiding, wherein the rotational movement of the motor is usually stepped down in order to permit a more fine touch control of the pump. With the application of stepper motors the interval between the motor steps for this is accordingly varied. The latter construction type is however relatively expensive on account of the motor and furthermore demands a complicated electronic control.

[0003] It is usual to provide an impulse control in order to adapt the flow to be delivered by the metering pump to another delivery flow (main delivery flow) with regard to time and quantity, in order to ensure a predetermined mixing ratio between these flows. For this metering pumps of both construction types usually have an input for an external impulse generator. At the same time a metering quantity to be set previously, i.e. a certain volume to be delivered by the metering pump, is allocated to each impulse of the external impulse generator which emits impulses in temporal intervals according to the throughput quantity of the main delivery flow. Whilst with the initially mentioned metering pumps with an electromagnetic drive this metering quantity to be delivered per impulse is usually set by the mechanical stroke adjustment, with electromotorically driven metering pumps this is exclusively possible by changing the stroke speed, thus the rotational speed of the drive motor.

[0004] Stepper motors and servo-motors with the controls necessary for this, as well as electric motors with a controllable rotational speed are comparatively expensive. One therefore makes do without the possibity of external impulse control with metering pumps with an electromotoric drive without rotary speed variation, thus those metering pumps of a simple construction type.

BRIEF SUMMARY OF THE INVENTION

[0005] Against this background it is the object of the invention to design a metering pump of the type according to the indtroductory part of claim 1 and operated with a drive not speed controllable, and whose stroke volume may not be changed, by way of simple means such that an external control by way of an impulse signal is also possible. In particular it is to be ensured that the delivery or admixing effected by the metering pump in no way exceeds the values predefined by the external control (impulse control).

[0006] According to the invention, this object is achieved by the features specified in claim 1. Advantageous formations of the invention are specified in the dependent claims as well as in the following description.

[0007] The basic concept of the present invention is that firstly a predefined delivery quantity is delivered by the pump when at least that many impulses have been registered by the control such that the metering quantity (nominal metering quantity) resulting from this is equal or larger than the preselected minimum delivery quantity of the pump.

[0008] A predefined part of an operating cycle may be selected as long as the metering pump is equipped with a position recognition which permits an allocation of the motor position to the stroke position of the pump, since then the quantity delivered by the pump in this operating cycle is defined. Preferably however the motor is not only activated to pass through a part of the operating cycle but in each case at least for passing through a complete operating cycle. The delivery quantity is then determined by the stroke volume of the pump. Such a control has the advantage that it may be realised without much technical effort, since with a suitable selection of the applied components one may completely do away with position determination of the motor and/or pump. If the operating cycle has been passed through completely once, at the beginning of the cycle independently of the motor/pump psoition at all events a complete pump stroke is carried out and thus at least the quantity is approximately delivered which the pump yields on a complete operating stroke. If for example it is the case of a membrane pump, as is usual with such pumps which is in the unloaded middle position when the control of the motor starts, then firsly half an operating stroke is passed, then a complete return stroke and then again the other half of an operating stroke so that in total the delivery quantity of a complete operating stroke is delivered.

[0009] The metering pump according to the invention may basically be operated with electric motors of different construction types, for example with a direct current motor or with an asynchronous motor. Advantageously a synchronous motor is applied as an electric motor, since then an electronic switch is sufficient for the motor control, in order to apply a predetermined alternating voltage, preferably the mains voltage, or to disconnect it from this. Since the synchronous motor runs at a constant speed given a predefined mains frequency, this is merely to be switched on for a predefined time in order to pass through a complete operating stroke. Since the gear between the electric motor and pump usually also contains a gear reduction, even with a pure time control one achieves a relatively high accuracy of the metering procedure, even if no position recognition is present.

[0010] Since the rotation of the motor is determined by the frequency of the supply voltage, it is particularly favorable not to control this according to a fixed time setting, but according to a predefined number of mains supply periods of the supply voltage. At the same time one may ensure that a high metering accuracy is effected without position recognition even with frequency fluctuations in the mains supply. Moreover the motor may be operated at 50 Hz or 60 Hz mains frequency without changes on the control side.

[0011] In order to further increase the accuracy of the metering, it is useful to equip the pump in a manner so that it may be calibrated. At the same time the actual quantity delivered by the pump in one operating cycle or where appropriate also part cycle is evaluated and stored in the control.

[0012] In the control a predetermined metering quantity (nominal delivery quantity) which preferably may be set on the control side is allocated to each external impulse. Within the control the incoming impulse and the metering quantities in each case resulting from these are added until the sum of the metering quantities has reached a value which is equal or larger than the delivery quantity of the pump in one operating cycle. Then the pump is activated in delivery. In the control one takes acount of the quantity which has been delivered by the pump in this operating cycle and accordingly subtracts this from the whole metering quantity. In this manner the remaining rest of the metering quantity is not lost, but is taken into account with regard to quantity. Reversely, in the control one also takes note if the delivery quantity of the pump remains below the metering quantity given by the impulse on account of the motor rotational speed limited by the mains frequency, in order yet to deliver this missed quantity when the temporal intervals of the impulses become larger again.

DETAILED DESCRIPTION OF THE INVENTION

[0013] For a better understanding, the invention is hereinafter described by way of example. A metering pump whose basic construction is for example known from DE 196 23 537 A1 is driven with a drive motor in the form of a synchronous motor. The motor drives a reduction gear which furthermore converts the rotational movement into a stroke movement which in turn drives the membrane pump. The membrane pump delivers 1 ml with on a complete pump stroke. One operating cycle of the pump consist of a return stroke with which the membrane pump suctions fluid into the pump chamber, and a working stroke with which the fluid located in the pump chamber is expelled under pressure. Since the gear is of a mechanical positive fit, a defined part stroke is allocated to each rotation of the motor. An operating cycle of the pump (return stroke and working stroke) thus corresponds to a number of motor revolutions pretermined by the mechanics. The synchronous motor which selectively may be operated at 50, 60 or even another mains frequency, comprises a control which determines an operating cycle of the pump by way of mains supply periods which have been supplied to the motor (i.e. in which the motor was conductingly connected to the mains supply). A defined rotational angle of the motor is allocated to each mains period and thus on account of the motor data and the known mechanical gearing ratios, without further ado one may determine how many mains periods are required so that the pump passes through a complete operating cycle. One therefore requires no position recognition for the pump or the motor since on passing through the complete operating cycle a quantity of 1 ml is always delivered. This quantity is evaluated previously by calibration and is inputted to the control.

[0014] If now this metering pump is to admix into a changing main delivery flow, then a synchronisation of the delivery quantities is required. For this one usually provides an impulse generator in the external main delivery flow which always outputs an impulse when the external main delivery flow has reached a predetermined quantity so that the metering pump delivers a suitable metering quantity, i.e. admixes to this main delivery flow. In the present example the metering quantity to be dispensed per impulse should be 0.3 ml.

[0015] If thus at the beginning of the delivery the control obtains the first external impulse, firstly a metering quantity (nominal delivery quantity) of 0.3 ml is stored in the motor control. It may then be checked whether the storage content corresponds to the quantity of 1 ml delivered by the pump in one operating cycle is larger. If this is not the case as in the previous example, then the metering quantity remains in the storage as a nominal delivery quantity.

[0016] On receipt of the next impulse firstly the metering quantity in the storage is increased by 0.3 ml, whereupon again it is compared as to whether the then resulting metering quantity of 0.6 ml is larger than or equal to the quantity of 1 ml delivered by the pump in one operating cycle. This is not the case so that the metering quantity remains in the storage.

[0017] When the fourth impulse is received the metering quantity in the storage has risen to 1.2 ml. Since this quantity is larger than the quantity of 1 ml delivered by the pump in one operating cycle, then the electric motor is activated by the control for the number of mains periods which corresponds to a complete operating cycle of the pump. Then the storage content is reduced by the delivered quantity of 1 ml so that there remains a metering quantity of 0.2 ml which then is taken into acount as well on receipt of the following impulse.

[0018] In this manner even with a simply constructed delivery pump (with synchronous motor and less complex motor control) one may effect a comparatively exact metering, in particular an adaptation to an external delivery flow. 

1. A metering pump with an electric motor, with a gearing downstream of this for converting the rotatory rotor movement into a translatory stroke movement, with an oscillating pump driven by this and with an electronic control, wherein the control activates the motor in dependence on an external impulse generator, wherein a predefined metering quantity is allocated to each impulse, and wherein the control activates the motor such that the motor, for passing through a predefined part of an operating cycle of the pump, is only activated when the control has received a number of impulses to which there corresponds a metering quantity which is equal or larger than the delivery quantity which the pump delivers in the predefined part of the operating cycle.
 2. A metering pump according to claim 1, wherein the control activates the motor for passing through a complete operating cycle of the pump when it has obtained a number of impulses to which there corresponds a metering quantity which is equal or larger than the quantity delivered by the pump in one operating cycle.
 3. A meterig pump according to one of the preceding claims, wherein the control evaluates a metering quantity according to the received impulses, and from this subtracts the already delivered quantity in order to determine the quantity yet to be delivered, and where appropriate to activate the motor in delivery.
 4. A metering pump according to one of the preceding claims, wherein the motor is a synchronous motor.
 5. A metering pump according to one of the preceding claims, wherein one determines an operating cycle by way of the mains periods of the supply voltage of the motor.
 6. A metering pump according to one of the preceding claims, wherein the delivery quantity of the pump may be calibrated in that the quantity delivered by the pump per operating cycle or part cycle is evaluated and stored in the control. 